Belief in God is rational.
Everything has a cause. So unless there is a first cause, then you would have an infinite regress. And then nothing could exist. Therefore there must be a first cause. Therefore God, the first cause, exists. QED. (You could prove the first step a priori that everything has a cause by noting that nothing can come from nothing. This makes it a priori, not just an empirical observation).

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29.1.17

The Republic (of Plato) is very important but not the sole basis for Western Civilization. The West was built out of the Mediaeval synthesis of Reason and Revelation. Plato and Aristotle form and important part of that. But so does the Law of Moses.[As Hegel noted this. The Jews gave devotion to the Law part of Western Civilization and Christians the compassion part.] What is the right synthesis is a good question, but that knowledge that such a synthesis is necessary is the condition for Western Civilization.[When Rambam talks about Metaphysics he is referring to Aristotle, but his understanding of Aristotle seems to me to be clearly the neo Platonic synthesis of Aristotle and Plato.]I am no scholar, but from the little I read I saw a great deal of the advancement of the West after 1350 was based on foundations that that were created during the Middle Ages.Things like parliamentary system of government, universities, water systems that became adapted to electricity, Thomas Aquinas, Maimonides were huge influences with Natural Law. I guess you could disagree but that is the way I see it. [It is my impression that Kant, and Hegel are as important for Western Civilization as Plato and Aristotle.]People do not give enough credit to the Middle Ages. The way to put Reason and Faith together is by no means simple as we can see in the many Gnostic schools and also in Philo and Plotinus. Just looking at that you get the idea that there were infinite possibilities of false and wrong and really dumb ideas about whether such a synthesis is possible and desirable at all and if it it then what is it? But only one possible right answer.